Prince is listed as playing the Umbria Jazz Festival in Perugia, Italy on July 15, 2011. It's up on the official website:

http://english.umbriajazz.com/mediacenter/FE/articoli/prince-at-umbria-jazz-11-friday-july-15.html

Damn, I lived there for 11 years, just moved back last year, and NOW he's coming!

Anyway, it's on the official Umbria Jazz website, so should be as definite as a Prince concert can ever be. Concert date is Friday, July 15, 2011. Looks like tickets go on sale June 6th.

He is probably playing at Santa Giuliana - a small outdoor stadium, where all the biggest acts play. It's a great festival. If you can go to the Prince concert, try to stay for an extra few days.